The present invention relates generally to acoustic warning or alerting systems, and more specifically to acoustic warning or alerting systems capable of producing highly directional audible sound.
Acoustic warning or alerting systems have been widely employed in a variety of applications. For example, acoustic alerting systems have been employed in vehicles such as automobiles, railroad trains, bicycles, airplanes, and boats for generating sounds to alert people and/or animals of the vehicle's presence. Specifically, horns have been used in automobiles for altering pedestrians of the automobile's approach. Further, horns, bells and/or whistles have been used on trains for altering people and/or animals on or near the railroad tracks of the train's presence. Similar acoustic alerting and alarm systems have also been employed in residential, industrial, and commercial settings, e.g., for generating sounds to warn individuals of dangerous conditions, and to alert intruders that they have entered restricted areas.
However, conventional acoustic alerting systems such as horns, bells, whistles, and alarms have drawbacks in that the sound generated by such systems is often not heard by the intended recipients. Even if the intended recipient hears the sound, he or she may not be sufficiently compelled to react to the sound in the most appropriate manner, such as by moving out of the path of an oncoming vehicle. For example, people who have survived being struck by a train frequently admit that they never heard the train coming until it was too late to move out of the train's way.
The effectiveness of conventional acoustic alerting systems has been enhanced somewhat by configuring them to generate more powerful or more attention-grabbing sounds such as louder or harsher sounds. However, because conventional acoustic alerting systems are generally omnidirectional, the loud and harsh sounds generated by such systems can usually be heard not only by the intended recipients, but also by people who have no need to hear the sounds. For example, although a train whistle is normally intended to be heard only by people and/or animals on or near the railroad tracks, in actuality, people who are a significant distance away from the tracks in all directions may hear the whistle. Specifically, when a train is travelling by a residential neighborhood, residents often complain about the loud warning sound of the train whistle as the train approaches road intersections, even though such warning signals are needed to avoid accidents. As a result, the number of trains allowed to pass, as well as the number of allowable train transit hours, may be severely curtailed near such residential neighborhoods.
Similar drawbacks exist for automobile horns, which are generally intended to be heard only by people and/or animals in front of the automobile. Because the sound generated by automobile horns typically radiates omnidirectionally, all people in the general vicinity of the automobile, including those who have no need to hear the horn, are often forced to listen to the sound. This can increase noise pollution to nuisance levels, especially in highly populated urban areas.
It would therefore be desirable to have an acoustic warning or alerting system that may be employed in a vehicle such as an automobile, a railroad train, a bicycle, an airplane, and a boat, and in residential, industrial, and commercial settings. Such a system would be capable of generating audible sound that is heard primarily by the intended recipient(s), instead of by everyone in the general vicinity of the system. It would also be desirable to have an acoustic alerting system that can generate highly directional sound that may be heard by both humans and animals.